Interscalene Block
The roots of the brachial plexus are found in the interscalene groove between the anterior and middle scalene muscles at the level of the cricoid cartilage (C6) in the neck. The interscalene groove is located lateral to the anterior scalene muscle and deep to the sternocleidomastoid muscle.
Transverse View of the Neck
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ASM = anterior scalene muscle
CA = carotid artery
IJV = internal jugular vein
MSM = middle scalene muscle
SCM = sternocleidomastoid muscle
Picture modified from Reg Anesth Pain Med 1998; 23: 77-80 |
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- Position the patient supine with the head turned 45 degrees to the contralateral side.
- After skin and transducer preparation (see Preparing Transducer for Single Shot), place a linear 38-mm, high frequency 10-15 MHz transducer firmly on the neck at the level of the cricoid cartilage in the axial, oblique plane to obtain the best possible transverse view of the brachial plexus.
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Transducer over left interscalene region
CL = clavicle |
- Optimize machine imaging capability by selecting the appropriate depth of field (within 2-3 cm), focus range and gain.
- Visualize the nerve roots or trunks in the transverse view (short axis). Nerves in the interscalene groove appear hypoechoic, distinctly round or oval, and are located between the anterior and middle scalene muscles. The internal jugular vein and carotid artery are visualized medially.
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Arrows indicate beam direction
Arrowheads = nerve roots
ASM = anterior scalene muscle
CA = carotid artery
IJV = internal jugular vein
MSM = middle scalene muscle
SCM = sternocleidomastoid muscle
White box = imaged region |
- Perform a systematic anatomical survey from medial to lateral and superficial to deep.
- The great vessels (carotid artery and internal jugular vein) serve as an easily identifiable point of reference.
- Medial to the great vessels, identify the thyroid gland and the trachea.
- Superficial to the great vessels is the triangular shaped sternocleidomastoid muscle.
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CA = carotid artery
SCM = sternocleidomastoid muscle |
- Lateral to the carotid is usually the internal jugular vein.
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IJV = internal jugular vein
CA = carotid artery
SCM = sternocleidomastoid muscle |
- Lateral to the great vessels is the anterior scalene muscle.
- The brachial plexus is visualized in the interscalene groove between the anterior and middle scalene muscles.
- Bring the roots/trunks into view by tilting/angling the transducer so that the beam is 900 to the nerves.
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ASM = anterior scalene muscle
Arrowhead = nerve root
MSM = middle scalene muscle
SCM = sternocleidomastoid muscle |
- Follow the nerves cephalad by moving the transducer to the upper interscalene region.
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Upper Interscalene Region (above C6)
ASM = anterior scalene muscle
Arrowheads = nerve roots
SCM = sternocleidomastoid muscle
TP = transverse process |
- Visualize the cervical nerve root (arrowhead) as it emerges from the neural foramen next to the transverse process (TP) (see figure above).
- The anterior scalene muscle is small in the upper interscalene location.
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Mid Level Interscalene Region (C6 level)
ASM = anterior scalene muscle
Arrowheads = nerve roots
SCM = sternocleidomastoid muscle |
- The ASM is now larger in size at this level and more nerve roots are seen in the interscalene groove (see figure above).
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Lower Interscalene Region (Below C6)
ASM = anterior scalene muscle
Arrowheads = nerve roots
SCM = sternocleidomastoid muscle
VA = vertebral artery |
- Move the transducer caudad to visualize branching of nerve roots (arrowheads) into trunks which travel superficially towards the skin surface (see figure above).
- The vertebral artery (VA) usually becomes visible below the C6 transverse process.
IN PLANE NEEDLE INSERTION APPROACH (LATERAL TO MEDIAL)
- Ultrasound guided interscalene block is considered a BASIC skill level block because this is a superficial block.
- For the in plane approach, insert a 5 cm 22G insulated block needle on the outer (lateral) end of the ultrasound transducer after skin local anesthetic infiltration. Advance the needle along the long axis of the transducer in the same plane as the ultrasound beam. This way, the needle shaft and tip can be visualized in real time as the needle is advanced towards the target nerves.
- Confirm the identity of the nerves by electrical stimulation if desired. Useful endpoints for shoulder surgery are deltoid or biceps muscle contraction for the interscalene block.
In Plane Approach - Needle in the Interscalene Groove
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ASM = anterior scalene muscle
Arrows = block needle
Arrowheads = nerves
MSM = middle scalene |
Out of Plane (OOP) Approach
- The OOP approach is another common approach for interscalene block and for interscalene catheter placement.
- For the OOP approach, align the target nerve with the midpoint of the transducer and then insert the block needle.
- Observe tissue and needle movement as the needle is advanced towards the target.
- Clear identification of the needle tip can be technically challenging.
- It is advantageous to inject a small volume of local anesthetic (1 mL) during needle advancement to facilitate tracking of the needle tip (see Needle Localization).
- Needle to nerve contact can be confirmed by electrical stimulation (if desired) and local anesthetic spread around the nerves.
The Effect of Head Turning
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SCM = sternocleidomastoid muscle |
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SCM = sternocleidomastoid muscle |
- In figure A, the sternocleidomastoid (SCM) muscle is noted to be overlying the interscalene groove (arrow = lateral end of SCM muscle) during OOP approach. Head rotation farther to the contralateral side will move the SCM muscle out of the needle path (as seen in figure B). The lateral end of the SCM muscle (arrow) is now medial to the interscalene groove (white dotted line).
- Observe the pattern of local anesthetic spread around the target nerves in real time during injection.
- Local anesthetic is seen as a hypoechoic fluid collection between the two scalene muscles.
- The usual volume of local anesthetic administration is between 15 (for analgesia only) and 40 mL (for surgical anesthesia).
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ASM = anterior scalene muscle
Arrows = block needle
Arrowheads = nerves
LA = local anesthetic
MSM = middle scalene |
- Avoid intramuscular injection which is indicated by an increase in echogenicity within the muscle bulk.
- Adjust the needle position during injection to optimize local anesthetic spread if necessary.
- Scan proximal and distal to assess the extent of local anesthetic spread.
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Post Injection
Nerves have a hyperechoic outline after injection and are clearly visualized.
Arrowheads = nerves |
- It is important to avoid local anesthetic injection immediately adjacent to the transverse process and the nerve root emerging from the neural foramen because of the risk of unintentional epidural or spinal anesthesia.
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Recommendation:
DO NOT inject at location # 1 since it is immediately next to the TP; injection at locations 2 and 3 is more appropriate.
Arrowheads = nerve roots
TP = transverse process |